<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<script>
			
			var A = {a:1,b:2,c:3,d:"hello world"};  
			for(let k in A) {  
			    console.log(k,A[k]);  
			} 
			
			/* var str;
			alert(str == undefined);
			alert(undefined == null);
			
			
			var result = NaN < 0;
			console.log(result); */
			document.write("null === undefined: " + (null === undefined) + "<br />");
			document.write("typeof undefined : " + typeof undefined + "<br />");	
			document.write(typeof null);
			
			var obj = {"key" : "1", "value" : "2"};
			var obj1 = {key : "100", value : "200"};
			console.log("obj -- key:" + obj.key);
			console.log("obj -- key:" + obj["key"]);
			console.log("obj1 -- key:" + obj1.key);
			console.log("obj1 -- key:" + obj1["key"]);
			/* var newObj = obj;
			newObj.value += obj.key;
			console.log(obj.value);
			 */
			
			
			/* var obj = {"key":"1","value":"2"};
			var newObj = obj;
			newObj.value += obj.key;
			alert(obj.value); */
			
			
			document.write("<p>你确定这就是<strong>爱</strong>吗？</p>");
			
			var a = //;
			// var b = ();
			document.write(a);
		</script>
	</head>
	<body>
	</body>
</html>
